An open natural gas leakage multiplex inspecting method and optical channel configuration, based on semiconductor laser absorbing spectrum method, relates to master case and open long optical channel system. The master case sets with electrical source socket, switch, fan, optical fiber linker and data transmission interface. The master case owns closed infrared semiconductor laser, semiconductor laser controller, phase-locked amplifier,signal generator,data collection disposal and control module, light switch, light switch driving circuit and infrared detector and connects with the locale optics system by optical fiber. Open optical system relates to integral optics telescope and more component angle reflector array and the former owns import optical fiber coupling implement and output optical fiber coupling implement. It achieves the time-sharing inspect of more gas component and more multiplex based on optical fiber distributing configuration of the light switch technology.